Field of the Disclosure
The present Disclosure relates to an image capturing apparatus and an image capturing system used in, for example, scanners, video cameras, and digital still cameras.
Description of the Related Art
Japanese Patent Laid-Open No. 2007-181088 discloses a technique to increase speed and reduce noise by a column signal amplifying unit with which gain is switchable, hold capacitance, and a noise removal circuit that has clamp capacitance with which a capacitance value is switchable. In the technique disclosed in Japanese Patent Laid-Open No. 2007-181088, in a mode in which a high operation speed is required, the capacitance value of the clamp capacitance is lowered, and time necessary for the clamping is shortened, thereby increasing the speed. On the other hand, in a mode in which a low noise is required, the capacitance value of the clamp capacitance is increased, and kT/C noise of the clamp capacitance is reduced, thereby reducing the noise.
Japanese Patent Laid-Open No. 2007-181088 has the following two problems. First, a signal amplified by a column signal amplifying unit attenuates due to a combined capacitance of the clamp capacitance and the hold capacitance. Second, a gain determined by the column signal amplifying unit and the noise removal circuit, and the capacitance value reduces noise cannot be determined independently.